1. Technical Field
The present invention relates to a concrete repair composition including an aggregate, a binder, and a fiber reinforcement.
2. Description of the Related Art
Concrete structures are structures predominantly made of cement, which is a hydraulic material that hydrates with water to generate a stable material. This hydration reaction produces an amount of calcium hydroxide equivalent to about one third of an amount of cement. Calcium hydroxide is a strong alkali having a pH of about 12 to 13, and forms a passive film on a rebar embedded in the concrete structures to prevent rebar corrosion, thereby maintaining the strength of the concrete structures.
However, the nature of concrete structures causes hairline cracks to form during initial curing. When water permeates into the cracks, the cracks in the concrete structures may grow by the repetition of freezing and melting of water depending on changes in temperature, which may remarkably reduce the durability of the concrete structures.
Particularly, when airborne salinity or an acidic substance such as carbon dioxide increasing in its level due to air pollution permeates into the concrete structures, the concrete structures may suffer from chloride-induced corrosion and carbonation. The corrosion may be accelerated by the rebar embedded in the concrete structures to maintain the strength of the concrete structures. In other words, when an acidic substance reacts with hydrate in concrete, in particular calcium hydroxide, the pH value of the concrete structures reduces below 10, accompanied by the breakdown of the passive film on the rebar, which causes the concrete structures to deteriorate by the likes of the rebar corrosion. By the rebar corrosion, the volume increases, which then applies tension to the surface of the concrete structures. Hence, the cracks on the surface of the concrete structures may grow to reduce the strength of the concrete structures.
As described above, concrete deterioration may progress under physical and chemical environment. Accordingly, extensive repair is needed.
To repair concrete, a variety of repair compositions have been used. Among them, there is cement mortar including an aggregate such as silica sand, a binder such as cement, and a fiber reinforcement such as glass fiber or carbon fiber. However, cement mortar has disadvantages of cracking during initial curing or delamination caused by poor bonding at the interface.
One of the most common defects that occur when repairing concrete is a defect generated at the interface between new concrete and deteriorated old concrete while curing since old dry concrete absorbs the moisture of fresh concrete after pouring, plastering, and spray coating. This causes a false-set problem, that is, rapid hardening of cement whereby cement just exists in the form of loose powder, failing to serve as a binder. As a result, a reduction in the interfacial bond between new concrete and old concrete leads to reduced bond strength, construction defects such as delamination, and the like.
To solve the foregoing problems, attempts have been continuously made to develop a concrete repair composition with good performance such as strength, alkali resistance, carbonization resistance, or water repellency.